Complementary metal oxide semiconductor image sensors generally utilize a series of photodiodes formed within an array of pixel regions of a semiconductor substrate in order to sense when light has impacted the photodiode. Adjacent to each of the photodiodes within each of the pixel regions a transfer transistor may be formed in order to transfer the signal generated by the sensed light within the photodiode at a desired time. Such photodiodes and transfer transistors allow for an image to be captured at a desired time by operating the transfer transistor at the desired time.
The complementary metal oxide semiconductor image sensors may generally be formed in either a front side illumination configuration or a back-side illumination configuration. In a front-side illumination configuration light passes to the photodiode from the “front” side of the image sensor where the transfer transistor has been formed. However, forcing the light to pass through any overlying metal layers, dielectric layers, and past the transfer transistor before it reaches the photodiode may generate processing and/or operational issues as the metal layers, dielectric layers, and the transfer transistor may not necessarily be translucent and easily allow the light to pass through.
In a back-side illumination configuration, the transfer transistor, the metal layers, and the dielectric layers are formed on a the front side of the substrate, and light is allowed to pass to the photodiode from the “back” side of the substrate such that the light hits the photodiode before it reaches the transfer transistor, the dielectric layers, or the metal layers. Such a configuration may reduce the complexity of the manufacturing of the image sensor and its operation.
However, without proper isolation between the various devices and transistors, the image sensor may not operate as efficiently as desired. In particular, as the size and pitch of pixels within an image sensor scale down, noise between the devices becomes more of a problem, and improper isolation can allow an undesirable junction leakage between the devices.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.